This invention relates to drive systems for power boats, and in particular to a new and improved dual drive package for operation between a motor and a pair of drive units mounted in the boat.
Several forms of drive units suitable for this use are shown in U.S. Pat. Nos. 4,565,532; 4,728,308; and 4,775,342.
In a typical dual drive package, there is an input shaft driven by the motor and a pair of output shafts connected to the drive units at the transom, with some form of gearing in the dual drive package for driving the two outputs from the input. There are a number of disadvantages with this configuration. The two output shafts are counter-rotating, and the spacing between the shafts is dictated by those gears which are available for the desired drive ratios. The output of most engines and the input of most drives (both stern drives and jet drives) all rotate in the same direction. If the direction of rotation of the output shafts are counter-rotating or rotating opposite to the engine, some additional complication must be included to correct this problem.
It is an object of the present invention to provide a new and improved dual drive package in which the input shaft is coupled to the output shaft by sprockets and chains, resulting in rotation of the two output shafts in the same direction. Also, the spacing between shafts is not dictated by the sprockets utilized so that selection of spacing and selection of drive ratios are independent of each other. Also, the vertical spacing of the axes of the shafts can be selected to accommodate the particular motor, hull and drive units being utilized. With the chain drive the vertical spacing can be modified independently of the spacing of the output shafts. With gears, as you change the vertical spacing of the input and output shafts you also affect (change) the spacing between the output shafts in order to maintain the single fixed gear centerlines.
A particular advantage utilizing the sprocket and chain drives lies in the fact that the axes of rotation for the output shaft can be varied slightly before or after installation by rotating the bearing housings for the output shafts a few degrees.
While propeller output drive units are shown in the above-identified patents and in the drawings of this application, the invention is equally applicable to jet drive units.
A problem sometimes encountered with dual drive packages is the possibility of a failure in one of the drive units, resulting in a substantial increase in load on the other drive unit. By way of example, with a motor providing 400 horse power at its output, the dual drive package normally would be designed to handle 200 horse power for each of the two drive units. When there is some failure in one of the drive units, the entire torque output of the motor is coupled to the still operating drive unit, which can result in serious damage.
There are several means of limiting the torque applied to the unit. One would be the shear pin. This would protect the unit from overloading, but would be unsatisfactory because the unit would become non-functional when the pin sheared. Another would be the slip clutch. This would allow the drive to still function, but would require additional complication to dissipate the heat from the slipping mechanism. The most satisfactory means of limiting the torque to the drive unit and still allow it to function is to provide a mechanism sensitive to the torque and a means of limiting the engine power to a predetermined, non-destructive torque level.
It is another object of the invention to provide such torque limiters which can be connected in line between the output of the dual drive package and the input of the drive unit, which torque limiters can function to reduce engine output when torque limiting is desired.
These and other objects, advantages, features and results will more fully appear in the course of the following description.